Many commercially available photoinitiators, including IRGACURE.RTM. 369, are presently used in ink compositions to accelerate ink drying in "radiation-drying printing." As used herein, the term "radiation-drying printing" refers to any printing method which utilizes radiation as a drying means. Radiation-drying printing includes, for example, off-set printing operations, such as on a Heidelberg press, flexographic printing, and flat-bed printing. Commercially available photoinitiator systems have a number of shortcomings. First, most of the commercially available photoinitiator systems require a relatively large amount of photoinitiator in the ink composition to fully cure/dry the ink composition. This leads to undesirable extractables within the ink composition. Second, most of the commercially available photoinitiator systems require a high energy radiation source to induce photocuring. Moreover, even with the high energy radiation source, often the cure results are unsatisfactory. Third, many commercially available photoinitiator systems are highly reactive to oxygen and must be used under a nitrogen blanket. Fourth, even with a large amount of photoinitiator and a high energy light source, the commercially available photoinitiator systems require a dry/cure time only accomplished by multiple passes, as many as 15 passes, under a light source, which significantly limits the output of a radiation-drying printing apparatus.
What is needed in the art is a new printing apparatus, which enables substantially instantaneous drying/curing of a photocurable ink without the need for a large amount of photoinitiator in the ink or a high energy radiation source for drying/curing. What is also needed in the art is a method of significantly increasing the output of a radiation-drying printing apparatus due to a reduction in ink drying/curing time.